Monoclonal antibodies specific for anthrax and peptides derived from the antibodies thereof

ABSTRACT

The present invention provides monoclonal antibodies which are highly specific for Bacillus spores. Also provided are peptides derived from those monoclonal antibodies. Both the antibodies and peptides are highly specific and can discriminate between spores of potentially lethal organisms such as  Bacillus anthracis  and other harmless but closely related bacilli and provide a very powerful tool in the construction of detection instruments as counter measures.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the fields of immunology andmicrobiology. More specifically, the present invention relates tomonoclonal antibodies specific for anthrax spores and peptides derivedfrom the antibodies.

2. Description of the Related Art

During the evolution of the immune system there is evidence that therepertoire of germline V genes that has been retained in the genome hasbeen subject to selective processes by environmental influences whichmay include self as well as commensal and non-commensal microorganisms.Structural and functional analysis of immunoglobulin and T cellreceptors have delineated regions of these molecules which are germlineencoded and have the ability to bind to certain bacterial componentsthrough exposed parts of the molecules which do not need somaticdiversification for expression of the ability to bind to thesestructures. Some of these included protein A binding to framework three(FR3) region of V_(H) genes, staphylococcal enterotoxin binding to Tcell receptor, etc.

The prior art is deficient in the lack of monoclonal antibodies whichare highly specific and can discriminate between spores of the Bacillusfamily including the strategically important B. anthracis. Further, theprior art is deficient in the lack of peptides derived from themonoclonal antibodies highly specific for Bacillus spores. The presentinvention fulfills this longstanding need and desire in the art.

SUMMARY OF THE INVENTION

The present invention is directed to monoclonal antibodies which arehighly specific for anthrax spores and peptides derived from theantibodies. The present invention demonstrated that the humoral immuneresponse to spores of Bacillus show a remarkable conservation of V_(H)gene usage which is distinct for each spore analyzed. The results implyevolutionary conservation of V_(H) genes due to their ability to bindspores. Furthermore, of highly practical importance, these antibodiescan discriminate between spores of potentially lethal organisms such asB. anthracis and other harmless but closely related bacilli and providea very powerful tool in the construction of detection instruments ascounter measures in biological warfare.

In one embodiment of the present invention, there is provided amonoclonal antibody specific for Bacillus spores. Preferably, Bacillusis selected from the group consisting of Bacillus anthracis, Bacillusthuringiensis, Bacillus subtilis and other bacilli related to Bacillusanthracis. Preferably, the antibody is IgG.

In another embodiment of the present invention, there is provided apeptide derived from the monoclonal antibody highly specific forBacillus spores.

In yet another embodiment of the present invention, there is provided amethod of preparing the monoclonal antibody highly specific for Bacillusspores by immunizing and fusing local lymph nodes of an animal.

In still yet another embodiment of the present invention, there isprovided a method of detecting Bacillus spores in a field sample using amonoclonal antibody highly specific for the Bacillus spores bycontacting the sample with a monoclonal antibody disclosed herein.

In still yet another embodiment of the present invention, there isprovided a method of detecting Bacillus spores in a field sample using apeptide derived from a monoclonal antibody highly specific for theBacillus spores by contacting the sample with a peptide derived from amonoclonal antibody highly specific for Bacillus spores.

Other and further aspects, features, and advantages of the presentinvention will be apparent from the following description of thepresently preferred embodiments of the invention given for the purposeof disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the matter in which the above-recited features, advantages andobjects of the invention, as well as others which will become clear, areattained and can be understood in detail, more particular descriptionsof the invention briefly summarized above may be had by reference tocertain embodiments thereof which are illustrated in the appendeddrawings. These drawings form a part of the specification. It is to benoted, however, that the appended drawings illustrate preferredembodiments of the invention and therefore are not to be consideredlimiting in their scope.

FIG. 1 shows antibodies with different reactivities for germinated andungerminated spores among different clones.

FIG. 2 shows that anti-spore monoclonal antibodies do not react withvegetative bacteria.

FIG. 3 shows that most antibodies react specifically with spores ofBacillus subtilis.

FIG. 4 shows that a commonly used member V_(H)7183.6 heavy chain gene ofthe V_(H)7183 (MOPC21) family in all hybridomas reactive with Bacillussubtilis spores appears to be the most unique member of this family inthe framework three (FR3) region. (Hybridomas g07 to f10 are labeled SEQID NO: 7 to SEQ ID NO: 17, respectively)

FIG. 5 shows that antibody-derived peptides specifically bind Bacillussubtilis spores.

FIG. 6 shows that anti-Bacillus anthracis antibody specifically bindBacillus anthracis spores.

FIG. 7 shows that the V_(H) gene sequences among monoclonal antibodiesto Bacillus anthracis. (SEQ ID NO: 18 to SEQ ID NO: 31)

FIG. 8 shows the discriminatory ability of the antibodies in vitro.Bacillus anthracis, Bacillus subtilis and Bacillus thuringiensis sporeswere mixed and stained on a slide with fluorescent antibodies labeledwith blue, green and red antibodies, respectively.

FIG. 9 shows the discriminatory ability of the antibodies in vivo. Asection of mouse spleen was injected 30 minutes previously with Bacillusanthracis, Bacillus thuringiensis, Bacillus subtilis spores and labeledwith blue, green and red antibodies, respectively.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, panels of monoclonal antibodies which arehighly specific and can discriminate between spores of the Bacillusfamily including the strategically important Bacillus anthracis(anthrax) were isolated and characterized. The amino acid sequences ofthese anti-spore antibodies were determined from the nucleotidesequences of the coding genes and smaller peptide molecules were derivedfrom these antibodies which can also bind Bacillus spores.

The present invention is directed to a monoclonal antibody highlyspecific for Bacillus spores. Preferably, Bacillus is selected from thegroup consisting of Bacillus anthracis, Bacillus thuringiensis, Bacillussubtilis and other bacilli closely related to Bacillus anthracis.Preferably, the antibody is IgG. The present invention is also directedto a peptide derived from the monoclonal antibody highly specific forBacillus spores. Preferably, the peptide can also bind the Bacillusspores specifically.

Also disclosed in the present invention is a method of preparing amonoclonal antibody highly specific for Bacillus spores, comprising thesteps of immunizing an animal with the Bacillus spores and fusing locallymph nodes of the animal.

The present invention also is directed to a method of detecting anthraxin a field sample using a monoclonal antibody highly specific forBacillus anthracis spores by contacting the sample with the monoclonalantibody and measuring the amount of binding of the antibody to thesample compared to an appropriate control.

The present invention also is directed to a method of detecting lethalBacillus spores in a field sample using the peptide derived from themonoclonal antibody highly specific for Bacillus spores by contactingthe sample with the peptide and measuring the amount of binding of thepeptide to the sample compared to an appropriate control.

The following terms have the definitions set below.

As used herein, “hybridoma” refers to a continuously growingantibody-secreting cell line derived from the fusion of a specificnormal antibody-forming B cell from an immunized mouse with an immortalmyeloma cell line. Hybridomas secrete monoclonal antibodies describedherein.

As used herein, “homogeneous staining” refers to the uniform staining ata similar intensity of all spores in a given sample.

As used herein, “heterogeneous staining” refers to the staining of oneor more populations of spores in a given sample.

As used herein, “unfixed untreated spores” refers to spores that are intheir native state in water and not treated with any kind of fixationreagent such as formalin or glutaraldehyde or paraformaldehyde.

As used herein, “two-color flow cytometric analysis” refers to theidentification of spore subpopulations or other particles byfluorescence activated flow cytometry using two independent fluorochromelabeled antibodies.

As used herein, “limiting dilution” refers to the distributing ofhybridoma cells into tissue culture plates such that less than 30% ofthe wells contain a growing clone. Each well, according to the Poissondistribution, should contain the progeny of only one cell.

The following examples are given for the purpose of illustrating variousembodiments of the invention and are not meant to limit the presentinvention in any fashion.

EXAMPLE 1 Animals

Eight to twelve-week-old BALB/c mice were purchased from Charles RiverLaboratories (Raleigh, N.C.) or bred in our mouse facility. BALB/c micewere used for immunization and obtaining feeder cells for subcloning ofhybridomas, phenotypic analysis and functional studies. Mice were housedin accordance with institutional policies for animal care and usage.

EXAMPLE 2 Bacterial Spores

B. subtilis spores were provided by Dr. Chuck Turnbough. B. anthracisspores were obtained from Dr. Joany J. Jackman at USAMIRID and B.thuringiensis spores were obtained from Abbott Laboratories.

EXAMPLE 3 Antibody Production: Immunization and Fusion

Six-week-old female BALB/c mice were inoculated with 5×10⁸ sporesemulsified in complete Freund's adjuvant at day 0, and then repeatedlywith spores in saline at days 3, 6, 9, 13, 17 and 20 in subcutaneoussites in the rear legs and inguinal regions.

On day 21, popliteal, inguinal and iliac lymph nodes draining sites ofinjection were removed, a lymphocyte suspension was prepared and fusedto P3x63Ag8.653 using a modification of the method described by Kohlerand Milstein. Fused cells were plated on ten 96-well plates in DMEMsupplemented with 20% fetal bovine serum (FBS), 2 mmol/L L-glutamine,HAT medium, and FCS (from HyClone Laboratories Inc., Logan, Utah; otherreagents from Sigma), and placed in a 37° C. incubator with 9% CO₂.

EXAMPLE 4 Primary Screening and Subcloning

Hybridoma supernatants were screened on spore suspensions usingtwo-color flow cytometric analysis. Binding of secreted mouse Ig fromsupernatants to the spores was traced with phycoerythrin (PE)-conjugatedgoat anti-mouse Ig (Southern Biotechnology Associates, Birmingham,Ala.). Data from stained cell samples were acquired using a FACScan orFACSCalibur flow cytometer with lysis II and Cell Quest softwarepackages (Becton Dickinson, Mountain View, Calif.) and analyzed withWinList 2.01 (Verity Software House, Inc.) and WinMDI 2.0 softwareprograms (Trotter@ scripps.edu).

EXAMPLE 5 ELISA

Flat bottom ELISA plates (E.I.A.A/2 plates, Costar) were coated withpoly-L-Lysine (50 μg) for 30 minutes and a suspension of spores at2×10⁸/ml (40 μl) in distilled water were allowed to dry on the platesovernight. Supernatants were added and after incubation developed withgoat anti-mouse Ig. Between each step, the plate was washed five timeswith PBS. The plate was developed with alkaline phosphatase substrate(Sigma, St. Louis, Mo.) (1 mg/ml) in substrate buffer (pH 9). Forquantitative ELISA, mouse antibody of known concentration was used as astandard in each plate and OD₄₀₅ values of plates were read by aTitertek Multiskan Plus MKII spectrophotometer (Flow, McLean, Va.).Antibody concentration was determined using an ELISALITE program(Meddata, New York, N.Y.).

EXAMPLE 6 Antibody Purification and Conjugation

Pure anti-spore antibodies were prepared from bulk hybridoma cultures byprotein G chromatography. FITC and phycoerythrin conjugates wereprepared using standard procedures.

EXAMPLE 7 Immunofluorescence and Immunohistochemical Analysis of TissueSections and Cytocentrifuge Preparations

Spleens embedded in OCT compound (Lab-Tek Products, Naperville, Ill.)were flash frozen in liquid nitrogen. Frozen sections were cut, airdried, fixed in ice-cold acetone, blocked with normal horse serum, andmacrophages stained with MOMA-1 (rat, IgG2a, 10 μg/ml, from Dr. GeorgKraal), each developed with biotin-conjugated goat anti-rat IgG (SBA).Next, the sections were blocked with normal rat serum followed byanti-spore reagents and secondary reagents and streptavidin AMCA (VectorLaboratories, Burlingame, Calif.). Spore suspension in distilled waterwere dryed onto poly-L-Lysine treated glass slides for 2 hours at 37°C., blocked with 1% BSA and PBS and stained with antibodies formicroscopy of spore suspensions.

Tissue sections and slides with dried spores were washed and mounted inFluormount G (SBA, Birmingham, Ala.) and viewed with a Leica/Leitz DMRBfluorescence microscope equipped with appropriate filter cubes(Chromatechnology, Battleboro, Vt.). Images were acquired with a C5810series digital color camera (Hamamatsu Photonic System, Bridgewater,N.J.) and processed with Adobe Photo Shop and IP LAB Spectrum software(Signal Analytics Software, Vienna, Va.).

EXAMPLE 8 DNA Sequencing Analysis

V_(H) and V_(K) gene sequencing was carried out from cDNA isolated fromhybridomas. To make cDNA, total RNA was isolated from hybridomas usingguanidinium thiocyanate-phenol-chloroform extraction. The cDNA wassynthesized using an oligo-dT primer followed by PCR using a Cμ 3′primer (SEQ ID NO: 1) and V_(H)7183-specific primer (SEQ ID NO: 2) forthe heavy chains or a Cκ 3′ primer (SEQ ID NO: 3) and a degenerate Vκ 5′primer (SEQ ID NO: 4) for the light chains. The PCR amplified DNA wascloned into Bluescript II KS and subjected to sequencing using aSequenase Kit (Strategene, La Jolla, Calif.). The DNA sequences wereanalyzed using the DNAstar program.

EXAMPLE 9 Antibodies to B. subtilis

Two immunization were made, one with fixed spores which gave only 3/192(1.6%) monoclonal antibodies (mAbs) reactive with spores; and the otherwith unfixed spores which gave 95/384 (25%) (mAbs) reactive with spores,another 89 (20%) weakly reactive. These 576 clones were then testedagainst other spore components and 15 reacted with NAD synthetase, 6with RNA polymerase, 5 with cot TC, 2 with SSPC, and 1 with cse60 byELISA. Totally, 136 clones were reactive with spores orpurified/recombinant components.

Among the clones reactive with the intact spores, certain patterns wereobserved: (1) two clones appeared to dramatically alter the FSC/SSCprofile of spores on flow cytometry; (2) some clones reacted withgerminated, but not with ungerminated spores; and (3) the majority hadhomogenous staining of germinated, but heterogeneous staining ofungerminated spores (FIG. 1).

96 clones of hybridomas reactive with B. subtilis were picked up andgrown on a new plate. They include two negative clones, the clonesreactive with purified proteins or peptides and clones reactive withspores representing different patterns. These antibodies were tested onthe vegetative forms of B. subtilis (i.e., live bacteria) and were foundto be negative (FIG. 2). They also did not react with two other speciesof spore-forming Bacilli (FIG. 3). Isotyping of the antibodies producedby these clones revealed that many (55/96) use λ light chains.Additionally, it was also unusual that 4 of these antibodies use α heavychains.

All 96 clones were subcloned by limiting dilution and tested by flowcytometry. 68/96 were still reactive with spores and all except one weremonoclonal. The reactive clones can be basically separated into twogroups: those reactive with all spores and the other reactive withsubsets of spores. Since these antibodies are of different isotypes,multiple parametric flow cytometric analysis could be done next. Theseimportant results showed that fixation of spores did not permitproduction of antibodies to the intact native spores and it was onlywhen unfixed untreated spores were used to immunize mice could manyhighly specific antibodies to B. subtilis be isolated.

EXAMPLE 10 Sequence Analysis of Monoclonal Antibody to B. subtilis

The striking over usage of λ light chains in the antibodies led tosequencing the heavy and light chains of the genes from hybridomassynthesizing the B. subtilis spore specific antibodies to obtain an ideaof the heterogeneity of antibodies generated. The heavy chains revealedremarkable homogeneity of V_(H) gene usage in that all hybridomas used amember of V_(H)7183 (MOPC21) family. This member V_(H)7183.6 appears tobe the most unique member of this family in the framework three (FR3)region as shown in FIG. 4. The CDR3 region was diverse in nearly allcases and used variable D_(H) and J_(H) genes. These results suggestthat there is a very strong selection for the use of this V_(H) genedespite the similarities inherent in the family members of this family.λ light chain sequence showed the exclusive use of Vλ1 Cλ1 withdifferent CDR3 regions. Six of these were selected for further study andcharacterization.

EXAMPLE 11 Isolation of FR3 Peptides which Bind to Spores

Based on the sequences of V_(H) genes utilized in antibodies againstBacillus subtilis spores, two peptides were designed: one correspondingto the consensus sequence of these antibodies in the framework 3 region(Peptide Anti-spore: SEQ ID NO: 5), and the other corresponding to theconsensus sequences of the 7183 V_(H) gene family to which theparticular V_(H) gene belongs (Peptide 7183 consensus: SEQ ID NO: 6).

The carboxyl-terminal cysteine was added for fluorochrome conjugation.Both peptides were conjugated with phycoerythrin, and tested for theirability to bind Bacillus subtilis spores. 7183 consensus peptide wasdesigned to be a control. It was found that the peptides derived fromthe anti-spore antibody stained brightly at 2 μg/ml (1 μM), while theconsensus peptide stained spores at 200 μg/ml (100 μM) (FIG. 5). Thusthe peptide derived from the spore specific nucleotide derived antibodysequence bind strongly and specifically to B. subtilis.

EXAMPLE 12 Serum Antibody Response to B. subtilis Spore Immunization

The immune response to Bacillus subtilis spores was characterized inmice. BALB/c mice were immunized with either spores or PBS (control).The mice were bled at 1, 2 and 3 weeks after immunization. Serumantibodies of different isotypes specific for spores were quantitatedusing ELISA. It was found that (1) immune responses peaked at 1 week;(2) light chain-containing antibodies account for about 30% of totalspore-specific immunoglobulin; and (3) in contrast to all otherisotypes, IgG3 antibodies continue to increase over the 3-week period.These findings confirmed the hybridoma analysis that the immune responseto B. subtilis spores is dominated by a particular set of B cell clones.

EXAMPLE 13 Monoclonal Antibodies to B. anthracis

Mice were immunized with a 50:50 mix of heavily irradiated (4×10⁶ Gy)Bacillus anthracis spores of the Ames and Sterne strains, generatedhybridomas, and screened for antibody production by FACS analysis. About60 hybridomas were selected for further characterization. A similarpattern of reactive antibodies was obtained with some of these panelsbinding 100% of B. anthracis spores. A seen in FIG. 6, a representativeprofile of more than 36 anti-anthrax antibodies which stain all sporesbut were not at all reactive with B. subtilis and B. thuringiensisspores. The V_(H) gene sequences were determined and are shown in FIG.7. Again a similar conservation in V_(H) usage was found similar to whatwas found in antibodies to B. subtilis. In this case, one of the twoV_(H) genes is from V_(H)7183 and the other from the V_(H)J558 familypredominates. A third V_(H) gene is from the V_(H)Q52 family.

EXAMPLE 14 Monoclonal Antibodies to B. thuringiensis

A similar strategy was used to isolate and characterize ˜100 antibodyforming hybridomas which reacted with B. thuringiensis. Again thepattern was similar with all reacting with B. thuringiensis but not B.subtilis or B. anthracis. These antibodies were cloned and aresequenced. The discriminatory ability of antibodies is shown in FIGS. 8and 9 where it is possible to clearly discriminate three distinct sporestaining by fluorescence in a mixture of the three kinds of spores invitro and in vivo.

EXAMPLE 15 Discussion

The work presented here disclosed panels of antibodies which are highlyspecific and can discriminate between spores of the Bacillus familyincluding the strategically important B. anthracis (anthrax). This isthe first time such antibodies have been isolated and characterized. Thereagents used in the various Divisions of the Armed services for testingwere not monoclonal. They were made in sheep and other species againstB. subtilis and B. anthracis.

The antibodies disclosed in the present invention are unique because ofseveral reasons: (1) the spores were not fixed with glutaraldehyde orformalin (which chemically modifies the spores) before immunization; (2)these are monoclonal antibodies made by immunizing and fusing locallymph nodes. Such a procedure has not been used in the past. The fewmonoclonal antibodies described before have been of the IgM isotypeswhich are more difficult antibodies to use and are more cross-reactive,i.e., react with spores other than B. anthracis, while the monoclonalantibodies disclosed herein are IgG. IgM antibodies of this kind areuseless in instruments designed to give positive results for anthraxspores in the field, since such antibodies will also detect harmlessspores such as B. subtilis which is ubiquitous in the environment.

The amino acid sequences of these anti-spore antibodies were alsoanalyzed, which allows one to design and make smaller peptide moleculeswhich can also bind spores. These will be more rugged molecules than thelarge antibody molecule and can be used in other kinds of detectors.Such peptides are totally unique in their binding to Bacillus spores.

There are numerous government (services and intelligence), as well asprivate groups trying to make instruments that are small, portable andhighly accurate in their detection of small numbers of potentiallylethal spores such as anthrax. The monoclonal antibodies presented herecould play a critical role in their instrument development program. Suchfindings will be significant in detecting air and water containinganthrax spores for civilian and military use.

Any patents or publications mentioned in this specification areindicative of the levels of those skilled in the art to which theinvention pertains. These patents and publications are hereinincorporated by reference to the same extent as if each individualpublication was specifically and individually indicated to beincorporated by reference.

One skilled in the art will readily appreciate that the presentinvention is well adapted to carry out the objects and obtain the endsand advantages mentioned, as well as those inherent therein. The presentexamples along with the methods, procedures, treatments, molecules, andspecific compounds described herein are presently representative ofpreferred embodiments, are exemplary, and are not intended aslimitations on the scope of the invention. Changes therein and otheruses will occur to those skilled in the art which are encompassed withinthe spirit of the invention as defined by the scope of the claims.

1. A isolated monoclonal antibody specific for the spores of anindividual species of Bacillus.
 2. The monoclonal antibody of claim 1,wherein said antibody is IgG.
 3. The monoclonal antibody of claim 1,wherein said Bacillus is selected from the group consisting of Bacillusanthracis, Bacillus thuringiensis, Bacillus subtilis, and bacillirelated to Bacillus anthracis.
 4. A peptide fragment of the monoclonalantibody of claim
 1. 5. The peptide of claim 4 binds Bacillus sporesspecifically.